The present invention relates to a photoelectric conversion device.
Heretofore a variety of applications of photoelectric conversion devices have been proposed. As an example of such an application, a contact image sensor for a facsimile machine is schematically illustrated in FIG. 1. The sensor is comprised of a photoelectric semiconductor layer 3 provided with a pair of electrodes 2 and 4 on the opposed surfaces, which are fabricated by lithography using three masks.
The fabrication method of this prior art device is as follows. First, a conductive layer of chromium is formed on a substrate 1 and patterned with a first mask 1m to form a plurality of first electrodes 2. Over the patterned electrode 2, a photosensitive intrinsic semiconductor layer of amorphous silicon is deposited to a thickness of 1 micrometer by a glow discharge method and patterned with a second mask 2m of a metal to form a photoelectric conversion layer 3. The amorphous silicon layer is formed in such a way that the patterned layer covers the first electrode 2 sufficiently even with a possible displacement of the mask 2m. Then, a conductive layer of indium tin oxide is formed on the semiconductor layer 3 and patterned with a third mask 3m to form a second electrode 4. A rectifying diode can be formed from a junction (MI junction) between the second electrode 4 and the semiconductor layer 3, i.e. a Schottky barrier.
When light is incident on the semiconductor layer 3 through the second electrode 4 as shown in FIG. 1(C), electron-hole pairs are generated in proportion to the intensity of the incident light.
The image sensor shown in FIGS. 1(A) to 1(C), however, is constructed with the semiconductor layer 3 larger than the first electrodes 2. Because of this, there are generated electron-hole pairs also in the region that is disposed vertically between the opposed electrodes 2 and 4 and lateral drifts of the carriers generated in the region take place. The lateral drift imparts a lag to the response.
On the other hand, the intrinsic semiconductor layer fabricated as described above tends to form a parasitic channel on an exposed surface thereof which is easily transformed into an n-type region, thereby causing a large dark current and dispersion in the quality of products. Further, the use of three masks reduces the cost effectiveness.